Heat exchanger

ABSTRACT

A heat exchange unit for hot gas heat recovery has a heat exchange array situated within a heat exchange duct defined between a cylindrical outer casing and an axially slidable inner sleeve. The sleeve, together with a plug valve at the upper end of the unit, forms a variable position sleeve valve arrangement which simultaneously controls the flow of hot gas through the heat exchange duct and the bypass duct.

FIELD OF THE INVENTION

This invention relates generally to heat exchangers having internalbypass arrangements which may be actuated to control the bypass of hotgas around a heat exchanger array and to direct gas flow into a bypasscircuit. It particularly relates to beat exchangers associated with gasturbines and gas/diesel engines for extracting heat from their exhaustgases.

BACKGROUND OF THE INVENTION

Heat exchangers of the type used to recover heat from gas turbine orgas/diesel engine exhaust gas are commonly designed with a bypasscircuit situated external to the heat exchanger array and its casing,with the exhaust gas flow to the heat exchanger array circuit and thebypass circuit controlled by one or two flap valves or the like, suchvalves being known as dampers. Arrangements are known in which a singledamper controls the flow through both circuits. Alternatively, twodamper arrangements are known, in which one damper controls the flowthrough the heat exchanger array circuit and the other damper controlsthe flow through the bypass circuit. Both types tend to be heavy, bulkyand complicated and when such dampers have been continuously modulatedfor continuously variable flow control reliability problems have beenexperienced. For example. with two damper arrangements, damage toengines has been caused by excessive back-pressure due to both dampersbeing closed at the same time, instead of one circuit always being open.

BRIEF DESCRIPTION OF THE INVENTION

According to the present invention, a heat exchange unit for exhaust gasheat recovery has heat exchange duct means, bypass duct means, heatexchange array means situated within the heat exchange duct means, and avariable position sleeve valve arrangement adapted to cause variableamounts of exhaust gas to flow through the bypass duct means instead ofthe heat exchange duct means, the heat exchange array means surroundingthe variable position sleeve valve arrangement and the latter definingthe bypass duct means and an inner wall of the heat exchange duct means,the variable position sleeve valve arrangement including sleeve meansmoveable axially of both duct means thereby simultaneously to controlflow of exhaust gas through the heat exchange duct means and the bypassduct means.

Preferably, the sleeve means is adapted to be axially continuouslymoveable between two extreme positions with respect to inlet means forthe heat exchange duct means and outlet means for the bypass duct means,whereby at one extreme position the inlet means for the heat exchangeduct means is open and the sleeve means obturates outlet means for thebypass duct means and at the other extreme position the sleeve meansobturates the inlet means for the heat exchange duct means and theoutlet means for the bypass duct means is open.

One benefit of the current invention is that the modulating sleeve valvemechanism is an integral part of the heat exchange unit, rather than aseparate piece of equipment, and is much simpler in its design than theprior art damper, making modulation more reliable. A further benefit isthe intrinsically safe nature of the sleeve valve arrangement, whereinit is not possible to close off both gas flow paths at the same time,thereby protecting the upstream equipment from overpressure damage. Afurther benefit is that the current invention is lighter and requiresless space than the prior art arrangements, which is of considerablebenefit in offshore applications.

Furthermore in the known designs it is usual for there to be a separatesound attenuator installed in the gas circuit either upstream or downstream of the heat exchanger unit. In the current invention it ispossible to favorably design the unit with sound attenuation linings onone or both sides of the sleeve means to damp sound in the bypass ductand/or the heat exchanger duct. It is possible also to provide thebypass duct with a flow splitter situated in the center of the sleevemeans, the flow splitter also having a sound attenuating lining on itssurface confronting the sleeve means. These measures would be intendedto eliminate the requirement for a separate attenuation device.

Further features and advantages of the invention will be apparent fromthe following description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is an elevation partly in section along the centerline of a heatexchanger unit in accordance with the invention, with an inner slidingsleeve valve shown positioned for passing hot gas through a heatexchanger array;

FIG. 2 is an elevation similar to FIG. 1 and showing the same heatexchanger unit, but with the sleeve valve shown positioned so that hotgas bypasses the heat exchanger array and passes through a centralpassage;

FIG. 3 is an elevation similar to FIG. 2, showing an alternativeembodiment of the invention;

FIG. 4A is a side elevation of the sleeve valve showing how it may beguided to slide up and down within the heat exchanger unit;

FIG. 4B is an enlarged view on section line B—B in FIG. 4A;

FIGS. 4C and 4D show in side elevation and sectional plan viewrespectively an enlarged detail of the guide mechanism, FIG. 4D being aview on section D—D in FIG. 4C; and

FIGS. 5 and 6 are sketches in part-sectional side elevation ofalternative embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The heat exchange units shown in the Figures are exhaust gas heatrecovery units suitable for use, e.g., in the offshore oil and gasindustries. The units are generally cylindrical in shape and are drawnwith their major axes oriented vertically. As indicated in FIG. 1, sucha unit is intended to receive hot gas 10 through gas inlet duct 34 froma gas turbine engine or other type of engine (not shown), cool the gasby heat exchange with a fluid circulating in a heat exchanger array 2,and pass the cooled gas 18 onwards for venting from the gas exit duct 7to a stack, or for further use. The heat exchange fluid 36 is passed inand out of the heat exchanger array 2 through concentric pipes 38. andcan be used as process fluid or for generating steam. or the like.

Referring to FIGS. 1 and 2 together, the heat exchange unit comprises agenerally cylindrical outer casing or shell 1, containing an annularheat exchanger array 2, an internal sleeve valve 3, and a valve plug 4.The sleeve valve 3 is slideable axially within the heat exchanger array2 between two extreme positions. In FIG. 1, the sleeve valve 3 is shownat its upper extreme position, so that the valve sleeve's centralpassage 19, termed a bypass duct, is effectively obturated, withsubstantially all the exhaust gas passing through the heat exchangerarray 2. In this position, the required gas seal to prevent flow throughthe bypass duct 19 is provided when an upper “knife edge” 14 of sleevevalve 3 buts against a valve seat 13 provided on the valve plug 4.

In FIG. 2 the sleeve valve 3 is shown at its lower extreme position,such that substantially all the hot gas 10 passes through the bypassduct 19, so bypassing the heat exchanger array 2. In this position, afrusto-conical valve seat 12 on the bottom of sleeve valve 3 forms a gasseal with a complementary frusto-conical valve seat 11 attached to theshell 1 below the heat exchanger array 2. so causing the hot gas 10 topass through the bypass duct 19 and out past the valve plug 4 throughthe annular opening 16 between the plug 4 and the outer components.

The plug 4 is supported at its axial position within the bypass duct 19,concentric with the shell 1, by means of a center post 40 which extendsalong the shell's longitudinal axis. Center post 40 is itself supportedfrom the shell 1 by means of struts 9 and 15 which are providedrespectively at the top and bottom of the center post 40. There shouldbe at least three struts at each of the top and bottom positions, thesestruts being equiangularly spaced around the assembly.

As shown particularly in the right-hand (non-sectioned) part of FIG. 1,the sleeve valve 3 is attached at its lower end to rods 20 for movingthe sleeve valve axially up and down within the heat exchanger unit. Therods pass through gas seals 17, and are actuated by one or moreactuation devices 9 attached to the gas inlet duct 22 by support plates30. The actuation devices 9 may be hydraulic, pneumatic, electrical, ormanually operated. For example. the rods 20 and hence the sleeve valve 3may be raised and lowered by means of ball screw devices on lead screwsdriven by electric motors. Again, there should be at least three rods20, each driven by an actuation device, equiangularly spaced around theassembly.

Advantageously, air 32 may be introduced into the lower heat exchangerspace 21 through gas seals 17, or alternatively into a space created bya multiple seated seal (not shown), for the purpose of performing asealing function by achieving complete isolation of the heat exchangercircuit from the hot gas 10. Additionally, or alternatively, such airmay be utilized to remove unwanted heat from the working fluid withinthe heat exchanger array 2 when the hot gas 10 passes only through thebypass duct 19.

For noise absorption within the heat exchanger duct, sound attenuationlinings 5 and 6 are provided respectively on the inside of the shell 1and on the outside of sleeve valve 3. The sound attenuation lining alsohas a temperature insulating function to reduce heat loss through thewalls of the heat exchanger duct.

FIG. 3 shows a preferred embodiment of the invention. As in FIG. 2, theunit is shown with the bypass duct in the extreme open position, buthere the valve plug 4 is provided with a downward extension 8 whichpasses axially through the bypass duct 19 concentric with the shell 1and center post 40. The extension 8 acts as a flow splitter and has acylindrical upper portion and a lower conical end portion. To provideimproved sound attenuation in the bypass duct 19, the outer surface ofthe cylindrical portion of the flow splitter 8, confronting the sleevevalve 3, has a sound attenuating lining 35 over at least part of itslength. Additionally, the lower part of the sleeve valve 3 is providedwith a sound attenuating lining 42 on its internal surface. However, thetop one fifth, approximately, of the sleeve valve 3 is not covered bylining 42, so as to avoid disturbing or restricting the flow of gasthrough the annular exit 16 of the bypass duct.

As shown in FIGS. 4A to 4D, lateral support of the sleeve, additional tothat provided by rods 20, is required to prevent undue vibration of thesleeve valve and can be achieved in a number of different ways. In thisembodiment the sleeve 3 is provided with three guide rails 24 secured toits external surface. These guide rails 24 extend lengthwise of thesleeve and are spaced 120 degrees apart around it. Similarly, the shell1 of the unit is provided with three guide rails 22 which confront therails 2. Dimensions are chosen so that there is a small clearance 44between the confronting surfaces of the rails. Pairs of guide plates 23are attached near the top and bottom of rails 22 and extend therefrom toembrace the rails 24 with a small clearance so as to prevent the rails24 on the sleeve 3 from moving out of registration with the rails 22 onthe shell 1. As shown in FIGS. 4A, 4C and 4D, the bottom portion of eachrail 24 on the sleeve 3 comprises a roller mechanism 25, in which aroller wheel 46 is free to run along the surface of rail 22 by rotatingon an axle 47. Axle 47 is held at each end by bearing plates 49, whichare attached to the upper end of a roller block 48. Block 48 is in turnattached at its upper and lower ends to the rail 24 through vibrationabsorbing joints 45. As will be seen from FIG. 4A, a similar rollermechanism is provided at the upper end of each rail 22 on the shell 1.Roller mechanism 25 ¹ differs from roller mechanism 25 only in that itsroller block 48 ¹ is attached to rail 22 and its roller runs along thesurface of rail 24.

FIGS. 5 and 6 sketch alternative embodiments of the invention toillustrate alternative methods of guiding the sleeve valve 3. In FIGS. 5and 6, similar items are given the same reference numbers as in FIGS. 1to 4 and will not be further described, since they differ only indetailed dimensions and shape.

In FIG. 5, the sleeve 3, shown in its lowest position, is guided by fourrods 53 connected at top and bottom to the outer casing 1. The valveplug 4 is also supported and by the rods 53 in order to align centrallywith the sleeve 3. The sleeve 3 is permitted to slide along the rods bytubular bearings 54 attached to the sleeve 3. An additional feature ofthis embodiment is that the valve plug 4 is permitted to slide a smalldistance axially up the rods 53 to provide a means of limiting the loadapplied to the sleeve 3 and plug 4 by the actuator devices 9. This is toprevent damaging the equipment in the event of excessive axial upwardmovement of the sleeve 3 for any reason.

In FIG. 6, the unit is shown with the sleeve 3 in its uppermostposition, i. e. with the bypass duct closed. In this embodiment, theplug seal 4 has a cylindrical extension 58 which extends axially downthrough the bypass duct 19 to a position below the valve seat 11. Thetop end of the plug 4 is laterally supported by plug support rods 55which are attached to the outer casing 1. The valve sleeve 3 is guidedand laterally supported from the plug 4 by two guide bearings 56.

Although FIGS. 1 to 6 above show the sleeve valve 3 in its two extremepositions, it should of course be understood that the position of thesleeve is variable according to the input from the actuators 9, so thatintermediate positions could be adopted. thereby allowing some of thehot gas 10 to pass through the bypass duct 19 and some through the heatexchanger array 2.

Furthermore, although in the above-described arrangements the sleeve 3defines both the bypass duct 19 and the inner wall of the heat exchangeduct, it would also be possible to have an inner structural wall,additional to the moveable sleeve 3, to perform the function of dividingthe bypass duct from the heat exchanger array.

There are other ways of arranging the internals of the heat exchangerapart from those shown in FIGS. 1 to 6 above which could be developedwithin the scope of this invention.

The casing 1, heat exchanger duct and internal bypass duct 19 arepreferably cylindrical, however, shapes having a non-circular crosssection are also functional.

The heat exchanger may also be configured to operate with the exhaustgas flowing in the opposite direction to that shown in the figures withonly relatively minor modifications to the internals.

The heat exchanger is most suited to operation in a vertical arrangementas shown in all figures, however, it may also be operated in any otherposition, including horizontal and upside down, again with relativelyminor modifications to the internals. The heat exchanger internals mayalso be altered to allow the plug to be situated at the other end of theheat exchanger, which may be beneficial in certain applications.

The position of the actuators and attachment of the actuator rods may bechanged from the lower end of the heat exchanger to the upper end.

The sleeve may be actuated and guided by alternative means to thosedescribed above and as shown in the Figures, again within the scope ofthis invention.

What is claimed is:
 1. A heat exchange unit with an intrinsically safe,internal bypass valve, comprising: a) an outer casing; b) a peripherallyand longitudinally extending, heat exchanger array; c) a sleeve valvemovable axially relative to the heat exchanger array and forming thebypass valve; d) a valve plug; e) an outer casing valve seat; and f)actuation means for moving the sleeve valve to create a gas seal on thevalve plug at one extreme of axial travel in order to cause a hot gas toflow through the heat exchanger array and, at an opposite extreme oftravel, to create a gas seal on the outer casing valve seat in order tocause the hot gas to flow through a bypass duct comprising a centralpassageway of the sleeve valve, thereby bypassing the heat exchangerarray.
 2. The heat exchange unit according to claim 1, including meansfor introducing sealing air to an annular space between the outer casingvalve seat and the heat exchanger array.
 3. The heat exchange unitaccording to claim 1, the heat exchange unit being arranged in serieswith an engine to receive exhaust gas therefrom.
 4. The heat exchangeunit according to claim 1, wherein the bypass duct includes soundattenuation linings to reduce sound levels emitted from the unit.
 5. Theheat exchange unit according to claim 1, wherein the bypass duct isprovided with a flow splitter to help guide the hot gas through theunit.
 6. The heat exchanger unit according to claim 5, wherein the flowsplitter comprises an extension of the valve plug.
 7. A heat exchangeunit for hot gas heat recovery, comprises: a) heat exchange duct means;b) bypass duct means; c) heat exchange array means situated within theheat exchange duct means; and d) a variable position valve arrangementadapted to cause variable amounts of a hot gas to flow through thebypass duct means instead of through the heat exchange duct means, theheat exchange array means surrounding the variable position valvearrangement, the variable position valve arrangement including sleevemeans movable axially of both the duct means for simultaneouslycontrolling flow of the hot gas through the heat exchange duct means andthe bypass duct means, the sleeve means being axially movable betweentwo extreme positions with respect to an inlet means for the heatexchange duct means and an outlet means for the bypass duct means,whereby, at one of the extreme positions, the inlet means for the heatexchange duct means is open and the sleeve means obturates the outletmeans for the bypass duct means and, at the other of the extremepositions, the sleeve means obturates the inlet means for the heatexchange duct means, and the outlet means for the bypass duct means isopen.
 8. The heat exchange unit according to claim 7, in which thesleeve means defines the bypass duct means and an inner wall of the heatexchange duct means.